 The intermixture of distinct species is guarded against by the aversion of the individuals composing them to sexual union, or by the sterility of the mule offspring. It does not appear that true hybrid races have ever been perpetuated for several generations,...  Life on the Earth: Its Origin and Succession - Página 178por John Phillips - 1860 - 224 páginasVista completa - Acerca de este libro
 | Charles Lyell - 1990 - 352 páginas
...beyond the defined limits being fatal to the existence of the individual. Sthly. The intermixture of distinct species is guarded against by the aversion...and not to the intermixture of hybrid with hybrid. 6thly. From the above considerations, it appears that species have a real existence in nature, and... | |
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